Field of the Invention
The present invention relates to a zeolite, a method for manufacturing a zeolite, a honeycomb catalyst, and an exhaust gas purifying apparatus.
Discussion of the Background
Conventionally, a SCR (Selective Catalytic Reduction) system in which ammonia reduces NOx to nitrogen and water is known as a system for converting exhaust gases discharged from automobiles. A CHA-structured zeolite (hereafter, also referred to as a CHA zeolite) with copper supported thereon is drawing attentions as a SCR-catalytic zeolite.
The SCR system includes a honeycomb unit having a large number of through holes longitudinally formed in parallel with one another for passing exhaust gases therethrough, as a SCR catalyst carrier. For example, WO 2012/086753 discloses a CHA-structured zeolite having a SiO2/Al2O3 composition ratio of less than 15 and a particle size of 1.0 to 8.0 μm with an aim of improving the heat resistance and durability when used as a SCR catalyst carrier.
JP-T 2012-508096 discloses a CHA-structured zeolite having a SiO2/Al2O3 composition ratio of less than 15 and an alkali content of less than 3% by mass. In this case, the CHA-structured zeolite coats the surface of a honeycomb unit base material made of another substance, thereby achieving SCR catalysis.
JP-A 2007-296521 discloses a technique in which a zeolite is extrusion-molded together with an inorganic binder and the like into a honeycomb shape in manufacturing of a honeycomb unit to be used as a SCR catalyst.